8,008 research outputs found
Response of carrot roots to wounding stress induced by processing: changes in chemical composition and enzyme activity.
In the present work both whole carrot roots and Cenouretes® from the cultivars Esplanada and Sugar Snax 54, were stored for 17 days at 5 ± 1.5 °C under dark or light conditions and evaluated after 2, 5, 8, 11, 14 and 17 days of storage
Resistivity study of the pseudogap phase for (Hg,Re) - 1223 superconductors
The pseudogap phase above the critical temperature of high
superconductors (HTSC) presents different energy scales and it is currently a
matter of intense study. The complexity of the HTSC normal state requires very
accurate measurements with the purpose of distinguishing different types of
phenomena. Here we have performed systematically studies through electrical
resistivity () measurements by several different current densities in
order to obtain an optimal current for each sample. This approach allows to
determine reliable values of the pseudogap temperature , the layer
coupling temperature between the superconductor layers , the
fluctuation temperature and the critical temperature as
function of the doping . The interpretation of these different temperature
scales allows to characterize possible scenarios for the (Hg,Re) - 1223 normal
state. This method, described in detail here, and used to derive the
(Hg,Re)-1223 phase diagram is general and can be applied to any HTSC.Comment: 31 pages, 12 figures, Latex; 25 pages, LaTeX; 11 figures; rewrited
section II and III; added 18 reference; rewrited title, added discussion
sectio
Ultra-pure digital sideband separation at sub-millimeter wavelengths
Deep spectral-line surveys in the mm and sub-mm range can detect thousands of
lines per band uncovering the rich chemistry of molecular clouds, star forming
regions and circumstellar envelopes, among others objects. The ability to study
the faintest features of spectroscopic observation is, nevertheless, limited by
a number of factors. The most important are the source complexity (line
density), limited spectral resolution and insufficient sideband (image)
rejection (SRR). Dual Sideband (2SB) millimeter receivers separate upper and
lower sideband rejecting the unwanted image by about 15 dB, but they are
difficult to build and, until now, only feasible up to about 500 GHz
(equivalent to ALMA Band 8). For example ALMA Bands 9 (602-720 GHz) and 10
(787-950 GHz) are currently DSB receivers. Aims: This article reports the
implementation of an ALMA Band 9 2SB prototype receiver that makes use of a new
technique called calibrated digital sideband separation. The new method
promises to ease the manufacturing of 2SB receivers, dramatically increase
sideband rejection and allow 2SB instruments at the high frequencies currently
covered only by Double Sideband (DSB) or bolometric detectors. Methods: We made
use of a Field Programmable Gate Array (FPGA) and fast Analog to Digital
Converters (ADCs) to measure and calibrate the receiver's front end phase and
amplitude imbalances to achieve sideband separation beyond the possibilities of
purely analog receivers. The technique could in principle allow the operation
of 2SB receivers even when only imbalanced front ends can be built,
particularly at very high frequencies. Results: This digital 2SB receiver shows
an average sideband rejection of 45.9 dB while small portions of the band drop
below 40 dB. The performance is 27 dB (a factor of 500) better than the average
performance of the proof-of-concept Band 9 purely-analog 2SB prototype
receiver.Comment: 5 page
Digital compensation of the side-band-rejection ratio in a fully analog 2SB sub-millimeter receiver
In observational radio astronomy, sideband-separating receivers are
preferred, particularly under high atmospheric noise, which is usually the case
in the sub-millimeter range. However, obtaining a good rejection ratio between
the two sidebands is difficult since, unavoidably, imbalances in the different
analog components appear. We describe a method to correct these imbalances
without making any change in the analog part of the sideband-separating
receiver, specifically, keeping the intermediate-frequency hybrid in place.
This opens the possibility of implementing the method in any existing receiver.
We have built hardware to demonstrate the validity of the method and tested it
on a fully analog receiver operating between 600 and 720GHz. We have tested the
stability of calibration and performance vs time and after full resets of the
receiver. We have performed an error analysis to compare the digital
compensation in two configurations of analog receivers, with and without
intermediate frequency (IF) hybrid. An average compensated sideband rejection
ratio of 46dB is obtained. Degradation of the compensated sideband rejection
ratio on time and after several resets of the receiver is minimal. A receiver
with an IF hybrid is more robust to systematic errors. Moreover, we have shown
that the intrinsic random errors in calibration have the same impact for
configuration without IF hybrid and for a configuration with IF hybrid with
analog rejection ratio better than 10dB. Compensated rejection ratios above
40dB are obtained even in the presence of high analog rejection. The method is
robust allowing its use under normal operational conditions at any telescope.
We also demonstrate that a full analog receiver is more robust against
systematic errors. Finally, the error bars associated to the compensated
rejection ratio are almost independent of whether IF hybrid is present or not
XTE J1946+274 = GRO J1944+26: An Enigmatic Be/X-ray Binary
XTE J1946+274 = GRO J1944+26 is a 15.8 s Be/X-ray pulsar discovered
simultaneously in 1998 September with the Burst and Transient Source Experiment
(BATSE) on the Compton Gamma Ray Observatory (CGRO) and the All-Sky Monitor
(ASM) on the Rossi X-ray Timing Explorer (RXTE). Here we present new results
from BATSE and {\em RXTE} including a pulse timing analysis, spectral analysis,
and evidence for an accretion disk. Our pulse timing analysis yielded an
orbital period of 169.2 days, a moderate eccentricity of 0.33, and implied a
mass function of 9.7 M_sun. We observed evidence for an accretion disk, a
correlation between measured spin-up rate and flux, which was fitted to obtain
a distance estimate of 9.5 +/- 2.9 kpc. XTE J1946+274 remained active from 1998
September - 2001 July, undergoing 13 outbursts that were not locked in orbital
phase. Comparing RXTE PCA observations from the initial bright outburst in 1998
and the last pair of outbursts in 2001, we found energy and intensity dependent
pulse profile variations in both outbursts and hardening spectra with
increasing intensity during the fainter 2001 outbursts. In 2001 July, optical
Halpha observations indicate a density perturbation appeared in the Be disk as
the X-ray outbursts ceased. We propose that the equatorial plane of the Be star
is inclined with respect to the orbital plane in this system and that this
inclination may be a factor in the unusual outburst behavior of the system.Comment: 18 pages, 15 figures, To appear in ApJ v584, Feb 20, 2003 issu
Revestimentos à base de carboximetilcelulose e conservação Pós-colheita de inflorescências de Heliconia bihai.
Low temperature structural phase transition and incommensurate lattice modulation in the spin gap compound BaCuSi2O6
Results of high resolution x-ray diffraction experiments are presented for
single crystals of the spin gap compound BaCuSiO in the temperature
range from 16 to 300 K. The data show clear evidence of a transition from the
room temperature tetragonal phase into an incommensurately modulated
orthorhombic structure below 100 K. This lattice modulation is
characterized by a resolution limited wave vector {\bf
q}=(0,0.13,0) and its 2 and 3 harmonics. The phase
transition is first order and exhibits considerable hysteresis. This
observation implies that the spin Hamiltonian representing the system is more
complex than originally thought.Comment: 4 pages, 4 figure
Efeito da refrigeração e da utilização do 1-MCP na longevidade pós-colheita de flores de Epidendrum ibaguense kunth.
Modeling the spread of cholera using human mobility estimates derived from mobile phone records
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